U.S. patent application number 12/204996 was filed with the patent office on 2008-12-25 for apparatus and system for well placement and reservoir characterization.
Invention is credited to Emmanuel Legendre, Jean Seydoux, Reza Taherian.
Application Number | 20080315882 12/204996 |
Document ID | / |
Family ID | 34864199 |
Filed Date | 2008-12-25 |
United States Patent
Application |
20080315882 |
Kind Code |
A1 |
Seydoux; Jean ; et
al. |
December 25, 2008 |
Apparatus and System for Well Placement and Reservoir
Characterization
Abstract
A resistivity array having a modular design includes a
transmitter module with at least one antenna, wherein the
transmitter module has connectors on both ends adapted to connect
with other downhole tools; and a receiver module with at least one
antenna, wherein the transmitter module has connectors on both ends
adapted to connect with other downhole tools; and wherein the
transmitter module and the receiver module are spaced apart on a
drill string and separated by at least one downhole tool. Each
transmitter and receiver module may comprise at least one antenna
coil with a magnetic moment orientation not limited to the tool
longitudinal direction. A spacing between the transmitter and
receiver module may be selected based on expected reservoir
thickness.
Inventors: |
Seydoux; Jean; (Houston,
TX) ; Legendre; Emmanuel; (Houston, TX) ;
Taherian; Reza; (Sugar Land, TX) |
Correspondence
Address: |
SCHLUMBERGER OILFIELD SERVICES
200 GILLINGHAM LANE, MD 200-9
SUGAR LAND
TX
77478
US
|
Family ID: |
34864199 |
Appl. No.: |
12/204996 |
Filed: |
September 5, 2008 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11160533 |
Jun 28, 2005 |
|
|
|
12204996 |
|
|
|
|
60587689 |
Jul 14, 2004 |
|
|
|
Current U.S.
Class: |
324/333 |
Current CPC
Class: |
G01V 3/28 20130101 |
Class at
Publication: |
324/333 |
International
Class: |
G01V 3/30 20060101
G01V003/30 |
Claims
1.-37. (canceled)
38. A modular downhole apparatus to determine a formation property,
the apparatus being incorporated into a drill string comprising one
or more downhole tools and drill pipe, the drill pipe being of the
same or various lengths, the modular downhole apparatus comprising:
a first module comprising a first drill collar having one or more
antennas mounted thereon or therein, wherein the first module has
connectors on both ends and is removeably connected to the drill
string; and a second module comprising a second drill collar having
one or more antennas mounted thereon or therein, wherein the second
module has connectors on both ends and is removeably connected to
the drill string; wherein a first dipole moment of one of the one
or more antennas of the first module intersects a first module
longitudinal axis at a first angle; wherein a second dipole moment
of one of the one or more antennas of the second module intersects
a second module longitudinal axis at a second angle; and wherein
the first and second angles are equal.
39. The modular downhole apparatus of claim 38, wherein the first
and second angles are non-longitudinal.
40. The modular downhole apparatus of claim 39, wherein the first
and second dipole moments are azimuthally offset from one
another.
41. The modular downhole apparatus of claim 38, wherein one of the
modules has an antenna having a third dipole moment that intersects
the longitudinal axis of that module at a third angle that is not
equal to the first angle.
42. The modular downhole apparatus of claim 38, wherein at least
one of the modules comprises a conventional resistivity tool.
43. The modular downhole apparatus of claim 38, wherein one or more
of the one or more antennas in one or both of the modules comprises
a transceiver.
44. The modular downhole apparatus of claim 38, wherein one or more
of the one or more antennas in one of the modules transmits a
signal and one or more of the one or more antennas in the other
module receives the signal.
45. The modular downhole apparatus of claim 38, wherein the one or
more antennas of one or both of the modules comprise transmitter
antennas and receiver antennas.
46. The modular downhole apparatus of claim 38, wherein one or more
of the one or more antennas of one of the modules is disposed
proximate to or within a drill bit.
47. The modular downhole apparatus of claim 38, wherein one of the
modules includes a drill bit.
48. The modular downhole apparatus of claim 38, wherein one of the
modules is part of a logging-while-drilling resistivity tool.
49. The modular downhole apparatus of claim 38, further comprising
one or more additional modules, each additional module having one
or more antennas, wherein each additional module has connectors on
both ends and is removeably connected to the drill string.
50. The modular downhole apparatus of claim 38, wherein one or more
of the one or more antennas in one or both of the modules comprises
a solenoid coil approximating a magnetic dipole.
51. The modular downhole apparatus of claim 38, wherein the one or
more antennas on the first module comprise a plurality of antennas
having dipole moments that intersect the first module longitudinal
axis at the first angle, and the one or more antennas on the second
module comprise a plurality of antennas having dipole moments that
intersect the second module longitudinal axis at the second
angle.
52. The modular downhole apparatus of claim 38, wherein the
formation property is one or more of a horizontal resistivity, a
vertical resistivity, a formation resistivity, a formation factor,
a fluid saturation, a dip angle, a dip azimuth angle, a porosity, a
distance to bed boundary, a formation conductivity tensor, or a
permeability.
53. A modular downhole apparatus to determine a formation property,
the apparatus being incorporated into a drill string comprising one
or more downhole tools and drill pipe, the drill pipe being of the
same or various lengths, the modular downhole apparatus comprising:
a first module comprising a first drill collar having one or more
antennas mounted thereon or therein, wherein the first module has
connectors on both ends and is removeably connected to the drill
string; and a second module comprising a second drill collar having
one or more antennas mounted thereon or therein, wherein the second
module has connectors on both ends and is removeably connected to
the drill string; wherein a first dipole moment of one of the one
or more antennas of the first module intersects a first module
longitudinal axis at a first angle; wherein a second dipole moment
of one of the one or more antennas of the second module intersects
a second module longitudinal axis at a second angle; and wherein
the first and second angles are unequal.
54. The modular downhole apparatus of claim 53, wherein the first
and second angles are non-longitudinal.
55. The modular downhole apparatus of claim 54, wherein the first
and second dipole moments are azimuthally offset from one
another.
56. The modular downhole apparatus of claim 53, wherein one of the
modules has an antenna having a third dipole moment that intersects
the longitudinal axis of that module at a third angle that is equal
to neither the first angle nor the second angle.
57. The modular downhole apparatus of claim 53, wherein at least
one of the modules comprises a conventional resistivity tool.
58. The modular downhole apparatus of claim 53, wherein one or more
of the one or more antennas in one or both of the modules comprises
a transceiver.
59. The modular downhole apparatus of claim 53, wherein one or more
of the one or more antennas in one of the modules transmits a
signal and one or more of the one or more antennas in the other
module receives the signal.
60. The modular downhole apparatus of claim 53, wherein the one or
more antennas of one or both of the modules comprise transmitter
antennas and receiver antennas.
61. The modular downhole apparatus of claim 53, wherein one or more
of the one or more antennas of one of the modules is disposed
proximate to or within a drill bit.
62. The modular downhole apparatus of claim 53, wherein one of the
modules includes a drill bit.
63. The modular downhole apparatus of claim 53, wherein one of the
modules is part of a logging-while-drilling resistivity tool.
64. The modular downhole apparatus of claim 53, further comprising
one or more additional modules, each additional module having one
or more antennas, wherein each additional module has connectors on
both ends and is removeably connected to the drill string.
65. The modular downhole apparatus of claim 53, wherein one or more
of the one or more antennas in one or both of the modules comprises
a solenoid coil approximating a magnetic dipole.
66. A method to determine a formation property, the method
comprising: providing a modular apparatus incorporated into a drill
string comprising one or more downhole tools and drill pipe, the
drill pipe being of the same or various lengths; the modular
apparatus comprising a first module comprising a first drill collar
having one or more antennas mounted thereon or therein, wherein the
first module has connectors on both ends and is removeably
connected to the drill string; a second module comprising a second
drill collar having one or more antennas mounted thereon or
therein, wherein the second module has connectors on both ends and
is removeably connected to the drill string; wherein a first dipole
moment of one of the one or more antennas of the first module
intersects a first module longitudinal axis at a first angle; a
second dipole moment of one of the one or more antennas of the
second module intersects a second module longitudinal axis at a
second angle; and the first and second angles are equal; using the
first and second modules to make measurements; and using the
measurements to determine the formation property.
67. The method of claim 66, further comprising using the formation
property to steer a drill bit.
68. A method to determine a formation property, the method
comprising: providing a modular apparatus incorporated into a drill
string comprising one or more downhole tools and drill pipe, the
drill pipe being of the same or various lengths; the modular
apparatus comprising a first module comprising a first drill collar
having one or more antennas mounted thereon or therein, wherein the
first module has connectors on both ends and is removeably
connected to the drill string; a second module comprising a second
drill collar having one or more antennas mounted thereon or
therein, wherein the second module has connectors on both ends and
is removeably connected to the drill string; wherein a first dipole
moment of one of the one or more antennas of the first module
intersects a first module longitudinal axis at a first angle; a
second dipole moment of one of the one or more antennas of the
second module intersects a second module longitudinal axis at a
second angle; and the first and second angles are unequal; using
the first and second modules to make measurements; and using the
measurements to determine the formation property.
69. The method of claim 68, further comprising using the formation
property to steer a drill bit.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This continuation application claims the benefit, under 35
U.S.C. .sctn. 120, of U.S. application Ser. No. 11/160,533, filed
on Jun. 28, 2005, which claims the benefit, under 35 U.S.C. .sctn.
119, of U.S. Provisional Application Ser. No. 60/587,689, filed on
Jul. 14, 2004.
BACKGROUND
[0002] 1. Field of the Invention
[0003] This invention relates to the field of subsurface
exploration and, more particularly, to techniques for determining
subsurface parameters and well placement. The invention has general
application to the well logging art, but the invention is
particularly useful in logging while drilling (LWD),
measurement-while-drilling (MWVD), and directional drilling
(Geo-steering) applications.
[0004] 2. Background Art
[0005] Electromagnetic (EM) logging tools have been employed in the
field of subsurface exploration for many years. These logging tools
or instruments each have an elongated support equipped with
antennas that are operable as sources (transmitters) or sensors
(receivers). The antennas on these tools are generally formed as
loops or coils of conductive wires. In operation, a transmitter
antenna is energized by an alternating current to emit EM energy
through the borehole fluid ("mud") and into the surrounding
formations. The emitted energy interacts with the borehole and
formation to produce signals that are detected and measured by one
or more receiver antennas. The detected signals reflect the
interactions with the mud and the formation. The measurements are
also affected by mud filtrate invasion that changes the properties
of the rock near the wellbore. By processing the detected signal
data, a log or profile of the formation and/or borehole properties
is determined.
[0006] The processing of the measured subsurface parameters is done
through a process known as an inversion technique. Inversion
processing generally includes making an initial estimate, or model,
of the geometry of earth formations, and the properties of the
formations, surrounding the well logging instrument. The initial
model parameters may be derived in various ways known in the art.
An expected logging instrument response is calculated based on the
initial model. The calculated response is then compared with the
measured response of the logging instrument. Differences between
the calculated response and the measured response are used to
adjust the parameters of the initial model. The adjusted model is
used to again calculate an expected response of the well logging
instrument. The expected response for the adjusted model is
compared with the measured instrument response, and any difference
between them is used to again adjust the model. This process is
generally repeated until the differences between the expected
response and the measured response fall below a pre-selected
threshold. U.S. Pat. No. 6,594,584 describes modern inversion
techniques and is incorporated herein by reference in its
entirety.
[0007] Well placement in real-time using resistivity measurements
has been used by the industry since the availability of LWD and MWD
tools. This application is commonly known as geo-steering. In
geosteering, estimation of the borehole position in real-time with
respect to known geological markers is performed through
correlation of resistivity log features. Because of the typical
close placement of the resistivity sensors of a LWD tool along the
drill collar, only limited radial sensitivity is attained, thereby
limiting the extent of the formation geological model knowledge and
estimation. Only with the introduction of sensors with transmitter
receiver distance in the tens of meters, a deeper radial
sensitivity can be obtained.
[0008] Schlumberger's LWD Ultra Deep Resistivity (UDR) induction
tool, with large transmitter receiver spacing in the tens of meters
has been successfully tested. One application of the tool has been
to determine the location of an oil-water contact (OWC) 7-11 m away
from the well path. U.S. Pat. No. 6,188,222, titled "Method and
Apparatus for Measuring Resistivity of an Earth Formation" and
issued to Seydoux et al., and U.S. patent application Ser. No.
10/707,985, titled "Systems for Deep Resistivity While Drilling for
Proactive Geosteering" by Seydoux et al., provide further
description of these tools and use thereof. The '222 patent and the
'985 application are assigned to the assignee of the present
invention and are incorporated by reference in their
entireties.
[0009] The LWD ultra deep resistivity basic tool configuration
comprises two independent drilling subs (one transmitter and one
receiver) that are placed in a BHA among other drilling tools to
allow large transmitter-receiver spacing. The basic measurements
obtained with this tool consist of induction amplitudes at various
frequencies, in order to allow detection of various formation layer
boundaries with resistivity contrasts having a wide range of
resistivities. The measurements are used to invert for an optimum
parameterized formation model that gives the best fit between
actual tool measurements and the expected measurements for the tool
in such a formation model.
[0010] FIG. 1 shows an example of an MWD tool in use. In the
configuration of FIG. 1, a drill string 10 generally includes kelly
8, lengths of drill pipe 11, and drill collars 12, as shown
suspended in a borehole 13 that is drilled through an earth
formation 9. A drill bit 14 at the lower end of the drill string is
rotated by the drive shaft 15 connected to the drilling motor
assembly 16. This motor is powered by drilling mud circulated down
through the bore of the drill string 10 and back up to the surface
via the borehole annulus 13a. The motor assembly 16 includes a
power section (rotor/stator or turbine) that drives the drill bit
and a bent housing 17 that establishes a small bend angle at its
bend point which causes the borehole 13 to curve in the plane of
the bend angle and gradually establish a new borehole inclination.
The bent housing can be a fixed angle device, or it can be a
surface adjustable assembly. The bent housing also can be a
downhole adjustable assembly as disclosed in U.S. Pat. No.
5,117,927, which is incorporated herein by reference. Alternately,
the motor assembly 16 can include a straight housing and can be
used in association with a bent sub well known in the art and
located in the drill string above the motor assembly 16 to provide
the bend angle.
[0011] Above the motor assembly 16 in this drill string is a
conventional MWD tool 18, which has sensors that measure various
downhole parameters. Drilling, drill bit and earth formation
parameters are the types of parameters measured by the MWD system.
Drilling parameters include the direction and inclination of the
BHA. Drill bit parameters include measurements such as weight on
bit (WOB), torque on bit and drive shaft speed. Formation
parameters include measurements such as natural gamma ray emission,
resistivity of the formations, and other parameters that
characterize the formation. Measurement signals, representative of
these downhole parameters and characteristics, taken by the MWD
system are telemetered to the surface by transmitters in real time
or recorded in memory for use when the BHA is brought back to the
surface.
[0012] Although the prior art deep-reading resistivity tools (such
as UDR) proved to be invaluable in geosteering applications, there
remains a need for further improved deep-reading resistivity tools
that can be used in geosteering and/or other applications.
SUMMARY
[0013] One aspect of the invention relates to a resistivity array
having a modular design. A resistivity array in accordance with one
embodiment of the invention includes a transmitter module with at
least one antenna, wherein the transmitter module has connectors on
both ends adapted to connect with other downhole tools; and a
receiver module with at least one antenna, wherein the transmitter
module has connectors on both ends adapted to connect with other
downhole tools; and wherein the transmitter module and the receiver
module are spaced apart on a drill string and separated by at least
one downhole tool. Each transmitter and receiver module may
comprise at least one antenna coil with a magnetic moment
orientation not limited to the tool longitudinal direction. In the
case of more than one antenna, all antennas orientation vectors may
be linearly independent. A set of vectors are linearly independent
if and only if the matrix constructed from concatenating
horizontally the vector's component has a rank equal to the number
of vectors.
[0014] Another aspect of the invention relates to resistivity
tools. A resistivity tool in accordance with one embodiment of the
invention includes a tool body adapted to move in a borehole; and
at least three modules (subs) disposed on the tool body, wherein
the at least three modules are not equally spaced along a
longitudinal axis of the tool body, such that a combination of the
at least three modules comprises a resistivity array of different
spacings.
[0015] Another aspect of the invention relate to resistivity tools.
A resistivity tool in accordance with one embodiment of the
invention includes a tool body adapted to move in a borehole; a
resistivity sensor disposed on the tool body and comprising a
plurality of modules forming at least one array; and an additional
antenna disposed on the tool body and spaced apart from the
resistivity sensor along a longitudinal axis of the tool body,
wherein the additional module and one of the plurality of module in
the resistivity sensor form an array having a spacing greater than
about 90 feet.
[0016] Another aspect of the invention relates to
logging-while-drilling tools. A logging-while-drilling tool in
accordance with one embodiment of the invention includes a drill
bit disposed at one end of a drill string; a first module disposed
on the drill string proximate the drill bit or in the drill bit,
and at least one additional module disposed on the drill string,
and spaced apart from the first module, wherein the first module
has at least one antenna with magnetic moment orientation not
limited to the longitudinal direction, and wherein the at least one
additional module comprises three antennas whose magnetic moment
orientations are linearly independent.
[0017] Another aspect of the invention relates to methods for
formation resistivity measurements. A method for formation
resistivity measurements in accordance with one embodiment of the
invention includes transmitting electromagnetic energy into a
formation using a transmitter antenna in a resistivity array,
wherein the transmitting is performed with a plurality of
frequencies according to a selected pulse scheme; and detecting,
for each of the plurality of frequencies, a signal induced in a
receiver antenna spaced apart from the transmitter antenna in the
resistivity array.
[0018] Another aspect of the invention relates to methods for
designing a resistivity array. A method for designing a resistivity
array in accordance with one embodiment of the invention includes
estimating a thickness of a reservoir; and disposing a transmitter
and a receiver on a drill string such that a spacing between the
transmitter and the receiver is no less than the estimated
thickness of the reservoir.
[0019] Other aspects of the invention will be apparent from the
following description and the appended claims.
BRIEF DESCRIPTION OF DRAWINGS
[0020] FIG. 1 shows a prior art drilling rig and drill string that
can be used with one embodiment of the invention.
[0021] FIG. 2 shows a resistivity array in accordance with one
embodiment of the present invention.
[0022] FIG. 3 shows a resistivity array in accordance with another
embodiment of the present invention.
[0023] FIG. 4 shows examples of depth of investigation for a 10 kHz
amplitude measurement obtained with various transmitter-receiver
distances in accordance with one embodiment of the present
invention.
[0024] FIG. 5 shows a resistivity array in accordance with one
embodiment of the present invention.
[0025] FIG. 6 shows a resistivity array in accordance with one
embodiment of the present invention.
[0026] FIGS. 7A and 7B show amplitude responses of conventional
prior art resistivity arrays.
[0027] FIGS. 7C and 7D show amplitude responses of resistivity
arrays in accordance with one embodiment of the present
invention.
[0028] FIG. 8 shows a sequencing method in accordance with one
embodiment of the present invention.
[0029] FIG. 9 shows a resistivity array in accordance with one
embodiment of the present invention.
[0030] FIG. 10 shows an antenna module in accordance with one
embodiment of the present invention.
[0031] FIGS. 11A-11F show various measurements for a planar
boundary with resistivity contrast according to one embodiment of
the invention.
DETAILED DESCRIPTION
[0032] Embodiments of the invention relate to resistivity arrays
having improved properties. Some embodiments of the invention
relate to methods of using these tools in formation evaluation.
Embodiments of the invention may permit inversion for more
complicated formation models (i.e., formation model with more
parameters) and/or may improve the robustness of resistivity
measurement inversion (uncertainty reduction). Some embodiments of
the invention may increase the flexibility of formation resistivity
evaluation by providing more measurements, each of which may have
different responses to different formation models.
[0033] Some embodiments of the invention provide resistivity arrays
having a modular design. The modular design facilitates setting up
different tool configurations for different measurement
requirements. For example, by extending the number of transmitter,
receiver combinations (for example, one embodiment with four
transmitters and one receiver, forming four transmitter-receiver
arrays), more depths of investigation can be obtained.
[0034] Some embodiments of the invention may include antennas that
can function as a transceiver (i.e., as a transmitter and a
receiver). This further provides tool configuration flexibility. In
this implementation, for the same number of modules, a greater
number of transmitter, receiver combinations can be achieved. Also,
symmetrization of directional measurement can be achieved, without
extending the length of the tool in a manner similar to the
published U.S. Patent Application No. 2003/0085707 A1, by Minerbo
et al.
[0035] Some embodiments of the invention relate to tools having a
transmitter sub at a great distance from the receiver (e.g., >90
ft) to allow selective sensitivity to reservoir complexity. Such an
embodiment may have an independently powered transmitter sub placed
outside (far away from) a conventional bottom hole assembly.
[0036] Some embodiments of the invention relate to placement of a
transmitter at or inside the drill bit, or very close to the drill
bit, for look-ahead capability. Such an embodiment may have an
independently powered system and data communication capability.
[0037] Some embodiments of the invention relate to having at least
one module located in a separate well or borehole
[0038] Some embodiments of the invention relate to methods of
formation resistivity evaluation using measurement frequencies
tailored to the expected formation. The frequency range, for
example, may be up to 200 KHz.
[0039] Some embodiments of the invention related to combining
modules of the invention with existing LWD resistivity arrays.
[0040] Some embodiments of the invention relate to coil designs
that have multiple windings to permit the use of the same antenna
for a wide range of frequencies. The multiple windings may be
connected in series or parallel.
[0041] Some embodiments of the invention related to extension of
the amplitude measurement to phase, relative phase and amplitude as
well as phase shift and attenuation (propagation) that requires a
sub to include two receiver antennas with relatively long spacing
in the ten feet range.
[0042] Some embodiments of the invention relate to implementation
of directional antennas (co-located or in close proximity) with or
without metallic shields.
Tool Modularity
[0043] Some embodiments of the invention relate to resistivity
arrays having modular designs. As used herein, a "resistivity
array" is a configuration that includes at least one receiver
module and at least one transmitter module attached at different
locations on a drill string. The modular design allows the
transmitter and receiver antennas to be placed at various locations
within a BHA, or at locations in the drill string above the BHA.
For example, FIG. 2 shows a resistivity array including four
transmitter modules 21, 22, 23, 24 and one receiver module 25
placed among other LWD or MWD tools 27, 28, 29, 30 in a BHA. By
inserting transmitter and/or receiver modules at different
locations on a standard BHA, as shown in FIG. 2, or a drill string,
specific depths of investigation can be implemented to optimize the
formation model inversion process that uses such deep resistivity
measurements. For example, in one embodiment, transmitter module 21
may be about 90 to 100 feet from receiver module 25. In addition,
one or more module may be placed in a nearby borehole to provide a
large spacing array.
[0044] The above-mentioned '985 application discloses an ultra-deep
resistivity array that may include transmitter and receiver
modules. The '985 application discusses the relationship between
depth of investigation ("DOI") and the spacing between a
transmitter and a corresponding receiver antenna, the relationship
being that greater spacing results in a corresponding increase in
DOI. The present inventors have found that the relationship holds
true; however, increasing the spacing complicates the ability for a
receiver to pickup and couple the signals from a transmitter.
Embodiments of the present invention may use a tri-axial antenna in
a transmitter or receiver module, wherein the tri-axial antenna
module has three antennas having magnetic moments in three
different directions. The tri-axial antenna module will ensure that
at least some of the transverse components of the tri-axial antenna
can form substantial coupling with the transverse component of a
corresponding transmitter or receiver. The use of a tri-axial
antenna transceiver (or receiver) is advantageous because when the
drill string is made up, it would be difficult to ensure that a
single antenna transmitter will align with a single antenna
receiver, with that difficulty increasing as the spacing increases.
In contrast, the tri-axial antenna transceiver (or receiver) will
always have a component substantially aligned with the magnetic
moment of a corresponding receiver (or transceiver) in the
resistivity array. In addition, tri-axial allows the determination
of formation characteristics such as dip angle, anisotropy,
shoulder bed effects.
[0045] FIG. 4 shows examples of depth of investigation for a 10 kHz
amplitude measurement obtained with transmitter-receiver distances
of 10, 30, 60 and 90 ft in the presence of a boundary with
resistivity contrast of 1 to 10 ohms. The drill string (hence the
resistivity array) is assumed parallel to the boundary and at
various distances away from the boundary. As shown in FIG. 4, the
10 ft array is not very sensitive to the boundary; it shows only a
slight magnitude changes in the vicinity of the boundary. The 30 ft
array is more sensitive, showing a distinct transition at the
boundary. The 60 ft array is even more sensitive; it shows very
pronounced resistivity transition around the boundary. At this
transmitter-receiver spacing, the signal magnitude starts to change
at about 20-40 ft away from the boundary. With the 90 ft array, the
signal magnitude change is even more profound. It is apparent that
combination of different depths of investigation allows
differentiations of geological formation at different radial
distance. The modular design makes it easy to configure the tools
for different array spacing. Further, the use of one or more
tri-axial antennas as transmitters and/or receivers increases the
spacing that may be achieved, which provides a corresponding
increase in DOI.
Modular Subs as Transceivers
[0046] Some embodiments of the invention relate to resistivity
array designs having transceiver antennas. In these tools, the
antennas are not designed as separate transmitters or receivers.
Instead, the same antenna can function as either a transmitter or a
receiver. Such enhancement, besides being economically
advantageous, allows more depth of investigation for the same
number of subs, as illustrated in FIG. 3.
[0047] FIG. 3 shows a tool assembly 40 having three subs 41, 42, 43
that form two arrays with spacing of D and Dx2. Because the
antennas 41 and 43 can function as a transmitter or a receiver, a
third array having a spacing of Dx3 is also available with this
tool configuration. Moreover, with the transceiver antennas,
directional measurements can also be performed without having to
have both transmitter and receiver belonging to a common downhole
tool. For example, a set of symmetrized measurements may be
obtained first with antenna 41 as the transmitter and antenna 43 as
the receiver, then with antenna 43 as the transmitter and antenna
41 as the receiver.
Remote Subs as Transmitter/Transceivers
[0048] Some embodiments of the invention relate to tools having
antenna subs placed far from other BHA tools (e.g., the receivers
or transmitters). Wells often have curves and bends that limit the
practical length of a BHA. Thus, conventional resistivity tools
cannot have transmitters and receivers spaced farther than the
practical length limit of the BHA (about 150 feet). Such tools
cannot provide the depth of investigation that might be needed when
placing a well path within a reservoir with a thickness that
exceeds the maximum practical length of a standard drilling tool
assembly.
[0049] FIG. 5 shows a resistivity array incorporating a remote sub
in accordance with one embodiment of the invention. As shown, the
resistivity array includes a conventional UDR 51 in the BHA. The
UDR includes three antennas (transmitters, receivers, or
transceivers) 52, 53, 54. Further up the drill string, the
resistivity array also includes a remote module 55, which includes
a transmitter, a receiver, or a transceiver. The antenna in the
remote module 55 may be used with any of the antennas 52, 53, 54 to
form an array having a large spacing. By using a remote module 55
with other conventional resistivity tools in the BHA,
transmitter-receiver distances (i.e., array spacing) can be set to
any desired distance. The remote module 55 may be independently
powered. Furthermore, the remote module 55 may be operated by
wireless telemetry, for example. In one embodiment, one or more
drill collars 63 may be located between the remote module 55 and
one or more of the antennas 52, 53, 54.
[0050] The location of the remote module 55 may be selected to be
on the order of (or greater than) the reservoir thickness. Having
an array spacing on the order of (or greater than) the reservoir
thickness can provide distinct advantages that are otherwise
unavailable to conventional resistivity tools.
[0051] For example, FIGS. 7C and 7D show that the amplitude
responses of the long array (the spacing of which is on the order
of the bed thickness, 130 ft) are much simpler and clearly indicate
where the bed boundaries are. The responses of this extra long
array (especially at low frequencies) are not sensitive to the
reservoir internal complexity. In contrast, as shown in FIGS. 7A
and 7B, the amplitude responses of conventional prior art
resistivity arrays (the spacing of which are smaller than the bed
thickness, 130 ft) are more sensitive to resistivity variations
within the bed, but less sensitive to bed boundaries. Results from
FIGS. 7A-7D show that sensor distances (array spacing) and
operational frequencies may be advantageously selected based on the
properties of the reservoir being drilled, for example, the
expected bed thickness or the ratio of the lowest reservoir layer
resistivity and the resistivity of the cap and reservoir
bottom.
Look-Ahead with Subs at the Bit
[0052] Some embodiments of the invention relate to resistivity
tools having look-ahead ability. In accordance with embodiments of
the invention, a sub may be placed proximate the drill bit in a way
similar to that described in U.S. Pat. No. 6,057,784 issued to
Schaff et al., and assigned to the assignee of the present
invention. That patent is incorporated herein by reference in its
entirety. In addition, an antenna can also be placed on a rotary
steerable tool or directly inside a bit. By placing a transceiver
at the bit, the resistivity measure point taken at the mid-distance
between each transmitter/receiver pair is moved closer to the bit,
thus allowing faster reaction time while drilling. This ability
allows earlier real-time action to be taken to place the well based
on geological events. Moreover, look-ahead of the bit is also
possible by using the tool response tail that extends beyond a
resistivity sensor pair.
[0053] FIG. 6 shows one example of a resistivity array in
accordance with one embodiment of the invention. As shown, the
resistivity tool 70 comprises a drill bit 14 at one end of the
drill string. An antenna 73 (which may be a transmitter or a
receiver antenna) is disposed on the drill string proximate the
drill bit 14. In addition, the resistivity array includes a UDR 51
having three transceiver modules 52, 53, 34, which can function as
receivers or transmitters. While three transceiver modules are
shown in this example, one of ordinary skill in the art would
appreciate that such a tool may have more or less transceiver
modules. Further, receiver or transmitter modules may replace one
or more of the transceiver modules. In one embodiment, antenna 73
may be a component of drill bit 14.
[0054] In accordance with some embodiments of the invention, the
near-bit antenna 73 has a non-longitudinal magnetic moment, i.e.,
the magnetic moment of the antenna 73 is not in a direction
parallel with the drill string axis. The non-longitudinal magnetic
moment of the antenna 73 ensures that the antenna 73 has a
component of the magnetic moment in the transverse direction (i.e.,
the direction perpendicular to the drill string axis). In addition,
at least one of the transceiver modules (e.g., 52, 53, 54)
comprises a tri-axial antenna, in which three antennas have
magnetic moments in three different orientations. In some cases,
the tri-axial antennas may have magnetic moments in three
orthogonal orientations. The tri-axial antenna module will ensure
that at least some of the transverse components of the tri-axial
antenna can form substantial coupling with the transverse component
of the near-bit antenna 73. The near-bit antenna 73 may be a
transmitter, receiver, or a transceiver. In general, it is
preferable for the near-bit antenna 73 to be a transmitter because
a receiver antenna may see higher electrical noise from increase
vibration and shock or from a possible presence of a high power
rotary steerable tool. As a result, the motor assembly 16, which
may include powered steering components, can disrupt a receiver
antenna.
Multi-Frequency Measurement
[0055] Some embodiments of the invention relate to tools and
methods that use multi-frequencies for resistivity measurements. In
accordance with embodiments of the invention, frequencies may be
selected to more efficiently cover the frequency spectrum in order
to improve the inversion accuracy and flexibility of deep
resistivity measurements. For example, in accordance with some
embodiments of the invention, measurements may be acquired with a
distribution of 3 or more frequencies per decade. These frequencies
can be set or automatically selected, either before drilling or
while drilling, to provide optimal formation inversion. The
combination of transmitter receiver distance with frequency is
integral in the determination of reservoir outer boundaries with
complex internal layer. The combination of antenna spacing and
frequency are preferably selected to respect the following equation
for maximum sensitivity.
[0056] Let's define propagation coefficient k as:
k.sup.2=.epsilon..mu..omega..sup.2+i.sigma..mu..omega., where
.epsilon. is the electromagnetic permittivity, .mu. electromagnetic
permeability, .sigma. conductivity, and .omega. the angular
frequency. If L represents the Transmitter-Receiver spacing, then
we want: |k|,L.epsilon.[0.1;10]. The frequencies are preferably
chosen to meet this criterion.
[0057] The multi-frequency measurements can be efficiently
performed using any implementation scheme known in the art. For
example, FIG. 8 shows an example of a resistivity measurement
sequence for multi-frequency measurement. In the scheme shown in
FIG. 8, all TX pulses are assumed to have a controlled amplitude.
Furthermore, one of ordinary skill in the art would appreciate that
in the pulse scheme, as shown in FIG. 8, a single pulse may be
implemented to carry two or more frequencies. Signal measurements
may be performed by measuring the true voltages as sensed by the
receivers. Alternatively, the signals may be measured as
differential signals between a pair of pulses of different
frequencies.
Combination of Subs with Existing LWD Tools
[0058] Some embodiments of the invention relate to resistivity
arrays having remote subs, as described above, with other
conventional resistivity tools. For example, FIG. 9 shows a tool
including two remote sub transmitters, 55A and 55B, and a
conventional LWD resistivity tool that may function as receivers
for the remote transmitter modules to provide arrays with spacing
much longer than what is possible with conventional resistivity
arrays. One of ordinary skill in the art would appreciate that any
conventional resistivity tool having one or more antennas for
receiving resistivity signals may be used in combination with
remote sub transmitters as disclosed herein. The option of running
transmitter modules in combination with an existing "shallow" LWD
tool (using their resistivity antennas as deep resistivity
receivers) allows asset rationalization and integrated measurement
capabilities.
Multi-Winding Antenna
[0059] Some embodiments of the invention relate to antennas that
may be used efficiently in a wide frequency range. When an antenna
is used to transmit a resistivity signal at a certain frequency,
the antenna is most efficient when the frequency is below the
self-resonance frequency of the antenna. Therefore, when a
particular antenna is used in a wide frequency range, the antenna
may not be efficient in certain frequency ranges. For example, to
transmit at the highest frequency, the number of turns in the
antenna should be low enough to be below the coil self resonance.
On the other hand, to be optimum in transmission at a lower
frequency, the number of turns needs to be increased. As a result,
conventional antennas often have windings that represent a
compromise for the intended operational frequency range.
[0060] In accordance with some embodiments of the invention, an
antenna may have several layers of windings; each of the layers may
be either wired in parallel for high frequency or in series for a
lower frequency to efficiently balance the impedance load of the
antenna when driven with a constant voltage. The switching between
serial and parallel configurations may be controlled
electronically.
[0061] FIG. 10 shows an exemplary antenna in accordance with one
embodiment of the invention. Coil layers 101A-101C, in this
example, are either connected in series to maximize the number of
turns in the transmission at low frequency (for example, around 1
kHz range), or are connected in parallel for the higher frequency
range (for example, 100 kHz). The coil layers 101A-101C are wrapped
around a mandrel 102. One of ordinary skill in the art would
appreciate that several layers of coils may be used in an antenna
to provide finer tuning of the performance of the antenna.
Extension to Other Resistivity Measurement Techniques
[0062] Conventional deep resistivity measurements, such as that
disclosed in U.S. Pat. No. 6,188,222, are based on induction
mechanism and measures signal amplitudes, not phase or phase shifts
or attenuations. Some embodiments of the invention relate to deep
resistivity measurements based on propagation mechanism and measure
phase shifts and attenuations (i.e., differential measurements), by
introducing an extra receiver antenna with a spacing between the
receiver pair on the order of 5 to 10 feet, which is significantly
longer than the receiver pair spacing (typically limited to less
than a foot) in a conventional propagation tool. The longer spacing
between the receiver pair is desirable because of the lower
frequencies used for deep EM measurement (1 to 200 kHz). A spacing
between the receiver pairs on the order of 5 to 10 feet would
ensure that the minimum phase shift that can be measured stays in
the 0.1 degree range.
[0063] In addition to using a receiver pair, differential
measurements in phase and amplitude (i.e., phase shifts and
attenuations) may also be performed with a proper pulse scheme,
such as that shown in FIG. 8. The measurement scheme shown in FIG.
8 may use one (or more) of the transmitted pulses at a specific
frequency as a time reference. Assuming a constant phase reference
(or time difference) between pulses in the pulse train (this time
difference can also be measured and communicated to the receiver
via wireless telemetry), the phase reference (or time difference)
for the received pulse trains can be determined with respect to the
reference pulse.
[0064] The same technique (using the amplitude of a reference pulse
for comparison) can also be applied to the amplitude ratio between
each pulse in the pulse train and the reference pulse. In this
case, the amplitude ratio at the transmitter may be kept constant
or measured. The difference technique in pulse time of arrival and
amplitude ratio reduces the dependence of the measurement on an
accurate air calibration as needed for the amplitude
measurement.
[0065] As an example, FIGS. 11A-11F show various measurements for a
planar boundary with resistivity contrast of 1 and 100 ohms, using
a tool having a transmitter-receiver spacing of 70 feet. This tool
has transmitter and receiver antennas that have longitudinal
magnetic moments (i.e., magnetic moments in a direction parallel
with the longitudinal axis of the tool).
[0066] FIG. 11A and FIG. 11B show amplitude measurements and
relative amplitude measurements, respectively, at various
frequencies. In FIG. 11B, the relative amplitude measurements are
with respect to the amplitude measurement at 2 KHz. FIG. 11C and
FIG. 11D show phase measurements and relative phase measurements,
respectively, at various frequencies. In FIG. 11D, the relative
phase measurements are with respect to the phase measurement at 2
KHz.
[0067] FIG. 11E and FIG. 11F show phase shift measurements and
attenuations, respectively, at various frequencies, as measured
with a pair receivers having an 8 feet spacing. With such a
spacing, significant variations in Phase Shift and Attenuation can
be readily observed. Both measurement provide another set of
measurements with a different sensitivity allowing more independent
measurements to be used during the inversion process.
[0068] Some embodiments of the invention relate to geo-steering. A
method of geo-steering in accordance with embodiments of the
invention may use any resistivity array described above and/or
using a measurement method described above (e.g., multi-frequency
measurements, use of a pulse schemes, etc.).
[0069] All measurements with the above-described embodiments of the
invention can be extended to directional measurements. Directional
measurements allow further sensitivity to the boundaries and will
improve the inversion process accordingly. In some embodiments, the
antenna(s) would have a transverse magnetic dipole combined with a
normal "axial" antenna to provide both measurements from the same
antenna. In a tri-axial antenna, as discussed above, one portion
may be aligned with the axis of the BRA, while the other two
portions are at angles relative thereto. Conventional shields can
also be implemented with embodiments of the invention as desired.
It will be appreciated that the antennas (and related electronics)
of the embodiments of the invention may be implemented using one of
many well-known antenna designs and packaging schemes. For example,
the logging apparatus described in U.S. Pat. No. 6,188,222 may be
used to implement the present invention.
[0070] While the above description uses logging-while-drilling
tools to illustrate various embodiments of the invention, a tool of
the invention is not limited by any particular mode of conveyance.
Therefore, a tool of the invention may be used in, for example,
logging-while-drilling, logging-while-tripping, coil drilling,
logging through the bit, liner drilling, casing drilling
operations.
[0071] While the invention has been described with respect to a
limited number of embodiments, those skilled in the art, having
benefit of this disclosure, will appreciate that other embodiments
can be devised which do not depart from the scope of the invention
as disclosed herein. Accordingly, the scope of the invention should
be limited only by the attached claims.
* * * * *